Morphotectonic evolution of the Jebel Bou Naceur in the South Middle Atlas Fault Zone (Morocco)

Abstract

International audienceIn eastern Morocco, fault-related folds develop above the South Middle Atlas fault that separates the J. Bou Naceur 'pop-up' structure and the Missour Basin, filled with alluvial sediments. Using a combination of surfaces, field observations and digital topographic information, we have investigated several geomorphic criteria and geometry of depositional surfaces governed by the relief's growth. The propagation of the deformation is recorded by warped segmented fans that moved southeastward and wellpreserved geomorphological features of tectonic origin. Uplift of the anticline hinges and acceleration of valley incision since the Late Pliocene are considered a consequence of the ongoing NW-SE convergence between Africa and Eurasia. A scenario of morphotectonic evolution of this active mountain front is proposed

Extracting dynamic topography from river profiles and cosmogenic nuclide geochronology in the Middle Atlas and the High Plateaus of Morocco

“…Laville et al (2007) and Delcaillau et al (2007) analyzed Quaternary deposits and knickpoints along major streams in the southern flank of the Middle Atlas, and interpreted them as related to recent thrust tectonic deformation, though they did neither quantify deformation rates nor discuss the potential role of regional uplift. The impresive 1000 m-high knickzone of the Chegg Ard river (Fig.…”

“…6) (Laville et al, 2007;Delcaillau et al, 2007). Four sets of fluvial deposits and abandoned alluvial fan surfaces were mapped along the Chegg Ard valley, which we have named T1…”

“…This mantledriven surface uplift is superimposed onto the tectonic effect of the thickened crust of the High and Middle Atlas produced by thrusting since the Paleogene. Although tectonic shortening is moderate in the Atlas thrust belts, deformation registered in Quaternary alluvial deposits at the southern fronts of the High and Middle Atlas indicates that thrusting is still active (Sebrier et al, 2006;Laville et al, 2007;Delcaillau et al, 2007;Pastor et al, 2012). Within this framework, the landscape of the foreland of the High and Middle Atlas (Arhbalou, Missour, and Guercif basins; Fig.…”

“…The southern Middle Atlas front defines the western margin of the Missour basin ( Naceur is unknown, but according to Laville et al (2007), the thrust system was active during the Neogene, when Mesozoic rocks were thrust over fluvial rocks of the Bou Irhardaiene Formation. Paleomagnetic data reported by Krijgsman and Langereis (2000) suggest that the deposit of the Bou Irhardaiene Formation lasted till the lower Pliocene (Zanclean).…”

“…Paleomagnetic data reported by Krijgsman and Langereis (2000) suggest that the deposit of the Bou Irhardaiene Formation lasted till the lower Pliocene (Zanclean). Thrust-related folding occurs in the northwestern margin of the basin and deforms the Bou Irhardaiene Formation and Quaternary alluvial gravels; the gravels are unconformable in some places (Delcaillau et al, 2007).…”